boost/libs/range/doc/reference/adaptors/type_erased.qbk

[/
    Copyright 2010 Neil Groves
    Distributed under the Boost Software License, Version 1.0.
    (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
/]
[section:type_erased type_erased]

[table
    [[Syntax] [Code]]
    [[Pipe] [`rng | boost::adaptors::type_erased<Value, Traversal, Reference, Difference, Buffer>()`]]
    [[Function] [`boost::adaptors::type_erase(rng, boost::adaptors::type_erased<Value, Traversal, Reference, Difference, Buffer>)`]]
]

Please note that it is frequently unnecessary to use the `type_erased` adaptor. It is often better to use the implicit conversion to `any_range`.

Let `Rng` be the type of `rng`.

* [*Template parameters:]
    * `Value` is the `value_type` for the `any_range`. If this is set to boost::use_default, `Value` will be calculated from the
        range type when the adaptor is applied.
    * `Traversal` is the tag used to identify the traversal of the resultant range. Frequently it is desirable to set a traversal category lower than the source container or range to maximize the number of ranges that can convert to the `any_range`. If this is left as boost::use_default then `Traversal` will be `typename boost::iterator_traversal<boost::range_iterator<Rng>::type>::type`
    * `Reference` is the `reference` for the `any_range`. `boost::use_default` will equate to `typename range_reference<Rng>::type`.
    * `Difference` is the `difference_type` for the any_range. `boost::use_default` will equate to `typename boost::range_difference<Rng>::type`
    * `Buffer` is the storage used to allocate the underlying iterator wrappers. This can typically be ignored, but is available as a template parameter for customization. Buffer must be a model of the `AnyIteratorBufferConcept`.
* [*Precondition:]  `Traversal` is one of `{ boost::use_default, boost::single_pass_traversal_tag, boost::forward_traversal_tag, boost::bidirectional_traversal_tag, boost::random_access_traversal_tag }`
* [*Returns:] The returned value is the same as `typename any_range_type_generator< Rng, Value, Traversal, Reference, Difference, Buffer >` that represents `rng` in a type-erased manner.
* [*Range Category:] __single_pass_range__
* [*Returned Range Category:] if `Traversal` was specified as `boost::use_default` then `typename boost::iterator_traversal<boost::range_iterator<Rng>::type>::type`, otherwise `Traversal`.

[heading AnyIteratorBufferConcept]
``
class AnyIteratorBufferConcept
{
public:
    AnyIteratorBufferConcept();
    ~AnyIteratorBufferConcept();

    // bytes is the requested size to allocate. This function
    // must return a pointer to an adequate area of memory.
    // throws: bad_alloc
    //
    // The buffer will only ever have zero or one
    // outstanding memory allocations.
    void* allocate(std::size_t bytes);

    // deallocate this buffer
    void deallocate();
};
``

[section:type_erased_example type-erased example]
[import ../../../test/adaptor_test/type_erased_example.cpp]
[type_erased_example]
[endsect]

This would produce the output:
``
1,2,3,4,5,
6,7,8,9,10,
11,12,13,14,15,
11,12,13,14,15,
``
[endsect]